If printing more than one page, the sheet before the fuser does have print on it.
The problem seems to lie at the top of the printer. I tested a print with the backdoor of the printer open, so that the paper exits there, and it printed perfectly well. As soon as it's closed and it pushes the paper to the output bin - same "jam" again! It just doesn't like exiting at the top of the printer!
I'll still have a look to see if I can find this flag though and make sure it's clean - can't hurt!